Variable resistor construction



Feb. 22, 1966 VARIABLE RES I S TOR CONSTRUCTION Original Filed Nov. 5, 1957 INVENTOR MARLANE. BOURNS FIG. 9

M. E. BOURNS 3,237,141

United States Patent 3,237,141 VARIABLE RESISTOR CONSTRUCTION Marlan E. Bourns, 2530 Piedmont Drive, Riverside, Calif. Continuation of application Ser. No. 695,086, Nov. 5, 1957. This application Aug. 26, 1963, Ser. No. 304,499 13 Claims. (Cl. 338180) The present invention relates to new and improved variable resistor constructions; and this application is a continuation of now abandoned application Serial No. 695,086 filed Nov. 5, 1957, which latter application is a continuation-in-part of application Serial No. 427,326, filed May 3, 1954, now Patent No. 2,831,949.

In .the leadscrew actuated type of potentiometer, or variable resistor, it is customary to mount the movable contact on a slidable carrier having a threaded hole through which the adjusting leadscrew is passed. Rotation of the leadscrew causes the carrier to be moved lengthwise of the resistance element in one direction or the other, depending upon the direction of rotation of the leadscrew.

Among the advantages of the leadscrew actuated type of potentiometer is its self-locking characteristic, which enables the potentiometer to maintain a position of adjustment despite severe acceleration or vibration, and its accuracy of adjustment, owing to the large mechanical advantage obtained by the screwthread drive. However,

this large mechanical advantage is also a detriment at times, since it is possible to damage the instrument irreparably if the leadscrew is forcibly turned when the contact carrier is abutting against the housing at either end of its travel. I

The primary object of the present invention is to provide a new and improved instrument of the class described, wherein a yieldable driving connection is provided between the leadscrew and carrier, so that the leadscrew can be forcibly turned when the carrier is unable to move further, without damaging the instrument.

A further object of the invention is to provide a contact carrier which can be assembled quickly and easily on the leadscrew, without the necessity of screwing the leadscrew through a threaded opening.

These objects are achieved by means of a spring member on the contact carrier, which engages the thread of the leadscrew to provide the driving connection between the leadscrew and the carrier. This spring member is yieldable under excessive stress and is capable of skipping or ratcheting over the thread of the leadscrew when the carrier is prevented from moving freely.

The foregoing and other objects and advantages of the present invention will become apparent to those skilled in the art, upon consideration of the following detailed description, together with the accompanying drawings, wherein:

FIGURE 1 is a side elevational view of a variable resistor embodying the principles of the invention;

FIGURE 2 is a cross sectional view of the same, taken at 22 of FIGURE 1;

FIGURE 3 is a cross sectional view, taken at 3-3 of FIGURE 2;

FIGURE 4 is a fragmentary sectional view, taken at line 44 of FIGURE 2;-

FIGURE 5 is another fragmentary sectional view, taken at 5-5 of FIGURE 2;

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FIGURE 6 is a perspective view of a slider employed in the construction of FIGURE 1;

FIGURE 7 is a perspective view of a contact member which is carried by the slider shown in FIGURE 6;

FIGURE 8 is a cross sectional view similar to FIGURE 3, showing a modified form of the invention;

FIGURE 9 is a similar cross sectional of still another form of the invention;

FIGURE 10 is a sectional view, taken at 10-10 of FIGURE 9; and

FIGURE 11 is a fragmentary sectional view, showing the manner of connecting one of the terminal lugs to the resistance element.

First to be described will be the embodiment shown in FIGURES 1 to 7, inclusive, of the drawings. The variable resistor is designated in its entirety by the reference numeral 10, and comprises a body 11 of nonconductive material such as plastic, ceramic, or the like, having a channel-shaped lid or cover 20 wrapped around three sides thereof. The body 11 is provided with a substantially fiat upper surface 12 and upstanding ends 14. The sides 15 of the body are recessed at 16 and 17 to receive the side walls 19 of the U-shaped cover 20. The top section 21 of the cover 20 is disposed generally parallel to the flat upper surface 12 between the ends 14 of the body member 11, and overlies the ends 14, to which it is secured by means of tabs 22 that extend down over the ends of the body within notches 23. At the bottom side of the body, the tabs 22 are turned under, as shown at 26, and are seated within cavities 25.

The upper surface 12 of the body 11 is provided with a longitudinally extending channel 30, in which is seated an inverted, U-shaped conductor 31 that serves as an electrical return means from the resistance element. Projecting downwardly from one side of the conductor 31 is a terminal tab 32, which passes through an opening 33 in the bottom of the body 11.

Parallel to the channel 30 is another channel 34, which holds a resistance element 36. The element 36 consists of resistance wire wrapped around a nonconductive card or mandrel 35, and the element is normally held in place by means of terminal tabs 37 projecting through apertures 38 in the bottom of the body 11. The tabs 37 are preferably bowed slightly, as shown at 39 in FIGURE 2 so that they are held within the apertures 38 by spring tension.

Disposed between the cover 20 and the body 11 is a slider, or carrier 40, having a U-shaped contact member 44 on the under side thereof which wipes on both the conductor 31 and resistance element 36. In the embodiment illustrated in FIGURES 1 to 7, the carrier 40 comprises a generally rectangular shaped block of nonconductive plastic, and is provided with an internally threaded bore 41 through which a leadscrew 50 passes. Also formed in the sides of the slider 40 are narrow, vertical slots 42 which receive upwardly projecting cars 43 of the contact member 44. The contact member 44 includes spring fingers 45, which wipe on the conductor 31 and element 36.

The leadscrew 50 is in the form of an elongated shaft having a threaded center section 51 and smooth ends 52 and 53. The end 52 is rotatably supported within a cavity 54 in the left-hand end 14 of the body; while the other end 53 is seated within a notch 56 in the righthand end 14 and projects beyond the end of the body. End 53 of the shaft is held against endwise movement by an inwardly projecting flange 57 in the notch 56, and

by means of a similar projection 58 (see FIGURE 4) extending downwardly from the top 21 of the cover 20. Projections 57 and 58 engage a shoulder, which may conveniently be provided by a circumferential groove 55 in the shaft 50.

At the other end of the shaft 50, a projection 59 extends downwardly from the top 21 of the cover and bears against the smooth portion 52, as best shown in FIGURE 5. Both of the projections 58 and 59 exert a slight pressure on the shaft so as to provide a certain amount of friction-a1 resistance to rotation. With this arrangement, the slider 40 and contact member 44 are moved lengthwise of the resistance element 36 and conductor 31 by rotating the leadscrew in one direction or the other. The slider 40 is prevented from turning with the shaft 50 by means of runners, or lugs 63, which project downwardly from the under side of the slider 40 and slidably engage the exposed sides of the conductor 31.

The modified construction shown in FIGURE 8 of the drawings differs from that shown in FIGURES 1 through in that the conductor and resistance element are in the form of a metal strip 64 and a strip 60 of resistive composition material or the like, both of which are disposed within parallel grooves 61 in the body member 11. Another difference in the construction of FIG- URE 8 is that the terminal tabs 62 are wedged within apertures 63 in the body 11, and include bent-over spring contact portions that overlie the conductor 64 and element 60, and make electrical contact with the top surfaces thereof. With this specific construction, the tab employed with the conductor strip 64 is located adjacent to one end thereof, so as not to interfere with the movement of the contact 44.

Another form of the invention is shown in FIGURES 9 and 10, which particularly illustrates a yieldable driving connection between the leadscrew and the slider 40. 'In this form of the invention, terminal tabs 65 are molded within the body 11 so as to project above the top surface 12, and are bent over at right angles to overlie films 66 (both of which may be resistance films, or one of which may be a film of silver ink or other highly conductive film) which are positioned upon supporting bases 67 of nonconductive material seated within slots 68. The tabs 65 may be soldered, as shown at 69, to the resistance film.

The slider 40 employed with the modified construction shown in FIGURES 9 and differs from those previously described, in that the bore 41 is somewhat oversize and is not threaded. Extending down into the slider 40 from the top side thereof is a cavity 71, which extends below and intersects the bore 41.

Seated within the cavity 71 is a V-shaped spring clip 72 having sides 73 and 74' that are joined at an apex 75. Both of the sides 73, 74 are provided with holes 76 and 77, respectively, which are of such a dimension that when the sides 73, 74 are bent together, the shaft 50 passes freely through the holes without having to screw the shaft through the holes, as is necessary with a threaded hole, such as in the embodiment of FIGURE 2. When the slider has been moved to the desired location along the length of the leadscrew, the sides 73, 74 are released, allowing them to spring outwardly. As the sides 73, '74 spread apart, the top and bottom edges of the holes 76, 77 grip the leadscrew on opposite sides thereof, and at least one of the said edges drops down into the thread of the screw portion 51 to provide a driving connection between the leadscrew and the slider. At the same time, the sides 73, 74 engage the edges 78 of the cavity 71 so as to wedge the spring clip 72 against the slider 40 in such a manner that as the shaft 50 is turned, the slider 40 is moved one way or the other along the length of the resistance element.

One advantage of the above-described arrangement is that it substantially eliminates backlash, since the thread of the leadscrew is resiliently gripped by the spring clip. Another advantage is that the sides 73, 74 of the spring clip are capable of yielding under excessive force, and ride up over the thread of the leadscrew. Thus, if the slider is moved to the end of its travel in either direction and is abutting against the body, it is impossible to damage either the body or the slider by forcibly turnmg the leadscrew.

Both of the sides 73, 74 terminate in bent-over end sections 79, which slidably engage the underside of the top section 21 of cover 20 to prevent the slider 40 from rotating when the shaft 50 is turned. The end sections 79 press against the cover 20 with a yielding spring pressure of sufficient force to resist the torque exerted on the spring clip 72 by the leadscrew.

While I have shown and described certain illustrative forms of the invention in considerable detail, it will be understood that various changes may be made in the shape and arrangement of the several parts without departing from the scope of the following claims.

I claim:

1. A variable resistor comprising a housing having a body, a resistance element mounted on said body, a threaded leadscrew rotatably supported on said body parallel to said resistance element, a slider mounted on said leadscrew and freely movable along the length thereof, means for providing a yieldable driving connection between said leadscrew and said slider includmg spring means having spaced-apart portions each engaging the thread of said leadscrew at a respective one of two longitudinally spaced-apart locations along the leadscrew whereby said slider and spring means are moved parallel to and adjacent to said resistance element when the leadscrew is turned, said spaced-apart portions of said spring means being constructed and arranged so that a first thereof slips relative to the thread of said leadscrew when said slider is prevented from moving freely in a first direction andthe second thereof slips relative to the thread of said leadscrew when said slider is prevented from moving freely in the opposite direction, and contact means on said slider wiping on said resistance element.

2. A variable resistor comprising a housing having a body, a resistance element mounted on said body, a threaded leadscrew rotatably supported on said body parallel to said resistance element, a slider mounted on said leadscrew and freely movable along the length thereof, said slider having a cavity formed therein, a V-shaped spring clip seated Within said cavity and having at least one edge thereof engaging the thread of said leadscrew, said spring clip being restrained against turning with respect to said slider, whereby rotation of said leadscrew causes said slider to move lengthwise thereof, and contact means on said slider wiping on said resistance element.

-3. A device of the class described, comprising a body, a resistance element mounted on said body, a slider positioned above said resistance element and movable along the length thereof, spring contact means carried by said slider and wiping on said resistance element, a rotatable screw shaft extending through an aperture in said slider, said slider having a transverse cavity intersecting said aperture, and a V-shaped follower of resilient sheet metal disposed within said cavity, the legs of said follower having aligned openings provided therein through which said shaft passes, said openings being of a dimension such that when the legs of the follower are pinched together, said shaft is freely movable therethrough, and when the legs are spread apart, the threads of the shaft are operatively engaged by opposite sides of said openings so that the carrier is shifted longitudinally by the threads when the shaft is rotated.

4. A variable resistor, according to claim 1, in which said spring means is a spring clip carried by said slider and normally disposed in acute angular relation to said leadscrew, said spring clip comprising first and second spaced-apart portions each normally engaging the thread of said leadscrew at a respective one of longitudinally spaced-apart locations thereon.

5. A leadscrew-adjusted potentiometer comprising in combination with an elongate resistance element and a rotary leadscrew disposed substantially parallel with the element,

first means comprising a contact disposed for longitudinal movement along and in electrical contact with said element incident to rotation-of the leadscrew within a normal range of rotation of the latter, second means constructed and arranged to impose first and second limits on longitudinal travel of said first means along said leadscrew, said first means comprising resilient spring means constructed and arranged to grip said leadscrew and engage the thread thereof at first and second spaced-apart locations for traverse longitudinally of the leadscrew incident to rotation of the latter, said spring means comprising opposed first and second limbs each disposed to engage said leadscrew at a respective one of said locations and each arranged for flexure toward and from the other, and said spring means being constructed and arranged to flex incident to imposition of one of said limits on travel of said first means, whereby said first means traverses longitudinally along said leadscrew between said limits incident to rotation of the leadscrew within a normal range of rotation of the leadscrew but discontinues traverse along the leadscrew incident to imposition of either of said limits and slips relative to the thread of the leadscrew despite continued rotation of the leadscrew outside said normal range of rotation. 6. A variable resistor comprising: first means, including a body and means cooperating with said body to provide an elongate structure having sides and ends; second means, including shaft means, said shaft means including a shaft having a center section having a thread, said shaft means having an end accessible from outside said structure whereby rotation may be imparted to said shaft, said first means including means rotatably supporting said shaft means in said structure; third means, including an elongate resistance element supported in said structure and having a surface disposed substantially parallel to said shaft means;

fourth means, including an insulative slider in said structure and arranged for movement therein toward and from either end thereof along said shaft;

fifth means, including contact means carried by said slider and having a contact disposed for contact with said surface of said resistance element;

sixth means, including V-shaped spring means insulated from said contact means and engaging said slider and engaging said thread of said shaft at two spacedapart points along said thread and providing a yielding connection therebetween whereby incident to rotation of said shaft said slider is moved along said shaft and said contact is moved along said resistance element in contact therewith and whereby incident to prevention of further movement of said slider along said shaft during continued rotation of said shaft said spring means is compressed and the spring means yields and skips over the thread to prevent damage to any of said means; and

seventh means, including conductive means and terminal means, providing electrical connections to said contact and said resistance element.

7. A variable resistor according to claim 6, said slider having an opening formed therein for reception of at least a part of said spring means and receiving therein the part of said shaft engaged by said spring means.

8. A variable resistor comprising:

a supporting structure, comprising a base, said supporting structure having opposed ends;

a shaft rotatably supported adjacent its ends by said ends of said supporting structure, said shaft comprising a section having a screw thread;

a resistance element supported by said supporting structure, said resistance element having a contact surface disposed substantially parallel to said shaft, and terminal connections to said resistance element;

a slider movable along said shaft between said ends of said supporting structure, said supporting structure comprising means for preventing substantial rotation of said slider with said shaft;

a contact device carried by said slider and having a contact engaging said contact surface of said resistance element;

a V-shaped spring device engaging said slider and having divergent portions engaging the thread of said shaft and normally serving to move said slider along said shaft incident to rotation of the shaft, said spring device being insulated from said contact and being compressed and yielding and skipping over the thread of the shaft incident to continued rotation of the shaft when continued movement of said slider along said shaft is prevented, whereby damage to the resistor incident to such continued rotation is avoided; and

conductive means in electrical connection with said contact for providing an electrical connection to said resistance element between said terminals.

9. A variable resistor according to claim 8, in which said slider is a block-like body of insulative material.

10. A variable resistor according to claim 8, in which said slider is formed with a recess in which recess a portion of said screw thread of said shaft is disposed and in which recess at least a portion of said spring device is disposed and in which recess said spring device engages said screw thread.

11. A variable resistor according to claim 8, in which said spring device comprises a portion disposed generally transversely of said shaft, said portion normally engaging the thread of said shaft and serving to move the spring device along the shaft incident to rotation of said shaft.

12. A variable resistor according to claim 8, in which said conductive means comprises a conductor generally parallel to said shaft, and a member integral with said contact arranged in conductive engagement with said conductor.

13. A variable resistor having a rotatable threaded shaft which resistor is adjusted by rotation of the shaft and which resistor comprises a resistance element disposed generally parallel to the threaded shaft, and an elongate electrical return conductor disposed parallel to said shaft, the variable resistor further comprising:

an insulative slider, said slider having a longitudinallyextending recess therein arranged for reception therethrough from end to end of a portion of the threaded shaft and for reception therein of at least the body portion of a spring device;

an electrical contact device carried by said slider for contact with the resistance element of the resistor and insulated from said shaft by said slider;

a yielding compressible spring device having a body portion disposed in said recess for engagement therein with the thread of the shaft, said spring device being insulated from said contact device and engaging said slider in said recess to nonmally move said slider therewith incident to rotation of said shaft, said spring device being adapted and arranged to compress and yield and skip over the thread of the shaft incident to continued rotation of the shaft when further movement of said slider is prevented, whereby damage to the variable resistor is avoided; and

7 6 terminal means providing electrical connections to said FOREIGN PATENTS contact via said conductor and to said resistance 668186 3/1952 Gmat Britain element. s

ANTHONY BARTIS, Primary Examiner.

References Cited by the Examiner UNITED STATES PATENTS RICHARD M. WOOD, Examiner. 1,692,962 11/1928 Thompson 338130 X R. F. STAUBLY, Assistant Examiner. 

1. A VARIABLE RESISTOR COMPRISING A HOUSING HAVING A BODY, A RESISTANCE ELEMENT MOUNTED ON SAID BODY, A THREADED LEADSCREW ROTATABLY SUPPORTED ON SAID BODY PARALLEL TO SAID RESISTANCE ELEMENT, A SLIDER MOUNTED ON SAID LEADSCREW AND FREELY MOVABLE ALONG THE LENGTH THEREOF, MEANS FOR PROVIDING A YIELDABLE DRIVING CONNECTION BETWEEN SAID LEADSCREW AND SAID SLIDER INCLUDING SPRING MEANS HAVING SPACED-APART PORTIONS EACH ENGAGING THE THREAD OF SAID LEADSCREW AT A RESPECTIVE ONE OF TWO LONGITUDINALLY SPACED-APART LOCATIONS ALONG THE LEADSCREW WHEREBY SAID SLIDER AND SPRING MEANS ARE MOVED PARALLEL TO AND ADJACENT TO SAID RESISTANCE ELEMENT 